The social/behavioral antecedents of adolescent drug use are identified and the effects of social skills training as a method of altering these antecedents are assessed. Hypotheses tested are that low levels of self-efficacy and assertive behavior are antecedents to initial gateway drug use; developmental transitions (age, grade, and school transition) affect self-efficacy, assertive behavior, and thus gateway drug use; and structured learning training improves the development of self-efficacy and assertive behavior and slows the development of gateway drug use. Subjects are students, 10 to 15 years old.